media/formats/mp2t/ts_section_psi.cc

   1 // Copyright 2014 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "media/formats/mp2t/ts_section_psi.h"
   6
   7 #include "base/basictypes.h"
   8 #include "base/logging.h"
   9 #include "media/base/bit_reader.h"
  10 #include "media/formats/mp2t/mp2t_common.h"
  11
  12 static bool IsCrcValid(const uint8* buf, int size) {
  13   uint32 crc = 0xffffffffu;
  14   const uint32 kCrcPoly = 0x4c11db7;
  15
  16   for (int k = 0; k < size; k++) {
  17     int nbits = 8;
  18     uint32 data_msb_aligned = buf[k];
  19     data_msb_aligned <<= (32 - nbits);
  20
  21     while (nbits > 0) {
  22       if ((data_msb_aligned ^ crc) & 0x80000000) {
  23         crc <<= 1;
  24         crc ^= kCrcPoly;
  25       } else {
  26         crc <<= 1;
  27       }
  28
  29       data_msb_aligned <<= 1;
  30       nbits--;
  31     }
  32   }
  33
  34   return (crc == 0);
  35 }
  36
  37 namespace media {
  38 namespace mp2t {
  39
  40 TsSectionPsi::TsSectionPsi()
  41     : wait_for_pusi_(true),
  42       leading_bytes_to_discard_(0) {
  43 }
  44
  45 TsSectionPsi::~TsSectionPsi() {
  46 }
  47
  48 bool TsSectionPsi::Parse(bool payload_unit_start_indicator,
  49                              const uint8* buf, int size) {
  50   // Ignore partial PSI.
  51   if (wait_for_pusi_ && !payload_unit_start_indicator)
  52     return true;
  53
  54   if (payload_unit_start_indicator) {
  55     // Reset the state of the PSI section.
  56     ResetPsiState();
  57
  58     // Update the state.
  59     wait_for_pusi_ = false;
  60     DCHECK_GE(size, 1);
  61     int pointer_field = buf[0];
  62     leading_bytes_to_discard_ = pointer_field;
  63     buf++;
  64     size--;
  65   }
  66
  67   // Discard some leading bytes if needed.
  68   if (leading_bytes_to_discard_ > 0) {
  69     int nbytes_to_discard = std::min(leading_bytes_to_discard_, size);
  70     buf += nbytes_to_discard;
  71     size -= nbytes_to_discard;
  72     leading_bytes_to_discard_ -= nbytes_to_discard;
  73   }
  74   if (size == 0)
  75     return true;
  76
  77   // Add the data to the parser state.
  78   psi_byte_queue_.Push(buf, size);
  79   int raw_psi_size;
  80   const uint8* raw_psi;
  81   psi_byte_queue_.Peek(&raw_psi, &raw_psi_size);
  82
  83   // Check whether we have enough data to start parsing.
  84   if (raw_psi_size < 3)
  85     return true;
  86   int section_length =
  87       ((static_cast<int>(raw_psi[1]) << 8) |
  88        (static_cast<int>(raw_psi[2]))) & 0xfff;
  89   if (section_length >= 1021)
  90     return false;
  91   int psi_length = section_length + 3;
  92   if (raw_psi_size < psi_length) {
  93     // Don't throw an error when there is not enough data,
  94     // just wait for more data to come.
  95     return true;
  96   }
  97
  98   // There should not be any trailing bytes after a PMT.
  99   // Instead, the pointer field should be used to stuff bytes.
 100   DVLOG_IF(1, raw_psi_size > psi_length)
 101       << "Trailing bytes after a PSI section: "
 102       << psi_length << " vs " << raw_psi_size;
 103
 104   // Verify the CRC.
 105   RCHECK(IsCrcValid(raw_psi, psi_length));
 106
 107   // Parse the PSI section.
 108   BitReader bit_reader(raw_psi, raw_psi_size);
 109   bool status = ParsePsiSection(&bit_reader);
 110   if (status)
 111     ResetPsiState();
 112
 113   return status;
 114 }
 115
 116 void TsSectionPsi::Flush() {
 117 }
 118
 119 void TsSectionPsi::Reset() {
 120   ResetPsiSection();
 121   ResetPsiState();
 122 }
 123
 124 void TsSectionPsi::ResetPsiState() {
 125   wait_for_pusi_ = true;
 126   psi_byte_queue_.Reset();
 127   leading_bytes_to_discard_ = 0;
 128 }
 129
 130 }  // namespace mp2t
 131 }  // namespace media
 132